A modular seal assembly that has become a standard device for positive, hydrostatic sealing of the annular space between a pipe or other conduit and a passage or casing through which the conduit extends, usually traversing a wall, is described in Barton U.S. Pat. No. 3,528,668 issued Sept. 15, 1970. Variations of that modular seal construction are disclosed in Barton U.S. Pat. No. 3,649,034 issued Mar. 14, 1972 and in Gignac U.S. Pat. No. 3,703,297 issued Nov. 21, 1972. These annular seals are each made up of a plurality of individual elastomer seal blocks faced with two sets of pressure plates. Bolts that interconnect the pressure plates may also join the blocks in a ring structure surrounding the conduit where it passes through a wall. The bolts are utilized to pull the pressure plates toward each other, once the annular seal structure is in place, compressing the elastomer seal blocks in a direction parallel to of the conduit and expanding the seal blocks radially outwardly in the space between the conduit and the wall passage or other passage. In this way a highly versatile and economical seal structure is formed with a single set of components that may be used for many different conduit sizes. Many years of rugged on-the-job use have demonstrated that this modular, annular conduit-to-wall-opening seal is far superior to most other seal structures.
Despite their proven versatility and value, the modular, annular seals of the aforementioned Barton and Gignac patents, particularly U.S. Pat. No. 3,528,668, have demonstrated some technical difficulties. In large sizes, particularly, the weight of the overall assembly is substantial and may make it difficult for workmen to install, especially due to the use of relatively large and heavy metal components in the pressure hardware that joins and expands/contracts the elastomer seal blocks. The pressure hardware, particularly metal components, have usually entailed non-standard members, so that costs tend to be higher than desirable. At the same time, the exposed metal, in some environments, may be susceptible to undesirable corrosion, particularly galvanic corrosion. The strength of the seal may be less than desirable in some instances. And perhaps the most important problem encountered with these seals pertains to consistency of the required expansion/contraction during installation. It has been difficult if not impossible to specify the tightening of the pressure hardware required to attain the desired positive sealing effect without over-stressing that hardware or some other component of the seal assembly.